Telephone service has been provided using Public Switched Telephone Networks (PSTN) also known as wired telephone networks and by the use of radiotelephones communicating over wide area cellular networks. Public cellular networks (public land mobile networks) are commonly employed to provide voice and data communications to a plurality of subscribers. For example, analog cellular radiotelephone systems, such as designated AMPS, ETACS, NMT-450, and NMT-900, have been deployed successfully throughout the world. More recently, digital cellular radiotelephone systems such as designated IS-54B in North America and the pan-European GSM system have been introduced. These systems, and others, are described, for example, in the book titled Cellular Radio Systems by Balston, et al., published by Artech House, Norwood, Mass., 1993.
Various devices and methods are known for remotely controlling accessories such as televisions and heating and air conditioning systems. These devices include line of sight devices such as infrared devices typically used with television remote controllers and simple RF links such as those typically used with garage door openers. These approaches generally suffer from limited range and marginal transmission performance. While special-purpose radio equipment could possibly be designed with high performance and long range, the costs of producing such products for remote control applications would be expected to be prohibitive. U.S. Pat. No. 5,548,635 to Bradley et al. describes a system for controlling equipment within a telephone subscriber's premises using Dual Tone Multiple Frequency (DTMF) signals. This allows for non-line of sight remote control of devices in locations served by wired telephone lines. The use of wired telephone lines to transmit remote control commands is also discussed in U.S. Pat. No. 4,885,766 to Yauoka et al., U.S. Pat. No. 5,386,461 to Gedney, U.S. Pat. No. 4,656,655 to Hashimoto and U.S. Pat. No. 4,353,502 to Myers.
DTMF signals are typically generated by pressing the keys on a modern "tone" type telephone (as contrasted with the older "pulse" systems). In addition to providing for communication of a phone number to be contacted to the public switched telephone network, various devices have been designed to utilize these audio frequency range DTMF signals for control such as voice mailboxes and answering machines.
One limitation of the various known methods for utilizing DTMF signals transmitted over telephone lines for remote control is that they generally require a telephone outlet in the vicinity of the device to be controlled. Accordingly, there are various locations which these approaches are unsuited for use, either because no wired telephone network exists or because no telephone outlet is available in the vicinity of the device to be controlled. Furthermore, the cost of making a wire line available in the vicinity of the device to be controlled may be prohibitive if the need for remote control is only occasional.